In the printing of natural or synthetic textile fabrics, the use of flat-bed and rotary screen printing has become quite prevalent. In these operations a screen defining the pattern to be printed is positioned over the textile (e.g. in the form of a fabric or carpet) and the dye paste is forced through the screen by a squeegee drawn across the screen. This procedure can be repeated with a sequence of screens and different colored print pastes to achieve the desired colored pattern on the substrate.
Screen printing procedures have imposed stringent performance requirements on the print paste formulations employed. These must be readily applicable to the fabric through the design screen to produce a clearly defined pattern and the resultant printing or design must be highly reproducible, preferably with a minimum of shut downs for maintenance of screens and squeegees.
The major constituents of the print pastes are a dye and water. Additionally, a chemical thickener is usually present to impart the desired viscosity to the print paste. Hydroxyalkylated cellulose, such as hydroxyethyl cellulose, is a commonly employed thickening agent in many applications, particularly in water-based compositions since the hydroxyalkyl group is hydrophilic. However, a problem has occurred in attempts to use hydroxyalkyl cellulose as a thickener in certain print paste formulations in that it has caused the formation of a water-insoluble sticky residue in the print paste. The formation of the residue resulted in clogging of the screens necessitating interruption of production operations in order to remove the residue from screens and squeegees.
The above described residue problem has been noted with a number of print pastes, but it is particularly severe when the print paste contains one of the so called "metallized" or "premetallized" dyes and especially when dyeing is carried out under conditions of low pH (i.e. on the order of about 2.0-5.0). As used herein the terms "metallized dye" or "premetallized dye" includes the acid metallized dyes and the neutral metallized dyes. In the carpet dyeing industry metallized dyes are frequently used and dyeing is frequently carried out under low pH conditions in order to obtain a high level of colorfastness, thus the residue formation problem is frequently encountered.
A further problem encountered with hydroxyalkylated cellulose is that it is sometimes difficult to dissolve in print pastes containing metallized dyes, requiring surfactants to be used to achieve a homogeneous composition.